wc-free-shipping-notice.php

<?php
/*
Plugin Name: WooCommerce - Free Shipping Notice
Plugin URI: http://www.damiencarbery.com
Description: Add note about free shipping for all except one product.
Author: Damien Carbery
Version: 0.1

*/

$exempt_product_id = array( 24, 1968 );

add_action( 'woocommerce_after_shop_loop_item', 'wfsn_free_shipping_notice_archive_7', 7 );
function wfsn_free_shipping_notice_archive_7() {
    global $post;
    global $exempt_product_id;
    
    if (in_array( $post->ID, $exempt_product_id ) == false) {
        echo '<p>woocommerce_after_shop_loop_item Priority 7; Product ID: ', $post->ID, '</p>';
    }
}

add_action( 'woocommerce_after_shop_loop_item', 'wfsn_free_shipping_notice_archive_15', 15 );
function wfsn_free_shipping_notice_archive_15() {
    global $post;
    global $exempt_product_id;
    
    if (in_array( $post->ID, $exempt_product_id ) == false) {
        echo '<p>woocommerce_after_shop_loop_item Priority 15; Product ID: ', $post->ID, '</p>';
    }
}


add_action( 'woocommerce_single_product_summary', 'wfsn_free_shipping_notice_single_25', 25 );
function wfsn_free_shipping_notice_single_25() {
    global $post;
    global $exempt_product_id;
    
    if (in_array( $post->ID, $exempt_product_id ) == false) {
        echo '<p><strong>woocommerce_single_product_summary Priority 25; Product ID: ', $post->ID, '</strong></p>';
    }
}

add_action( 'woocommerce_single_product_summary', 'wfsn_free_shipping_notice_single_60', 60 );
function wfsn_free_shipping_notice_single_60() {
    global $post;
    global $exempt_product_id;
    
    if (in_array( $post->ID, $exempt_product_id ) == false) {
        echo '<p><strong>woocommerce_single_product_summary Priority 60; Product ID: ', $post->ID, '</strong></p>';
    }
}

Change $exempt_product_id to an array and change the test to in_array().